This invention relates to a process for making a granular detergent product and the product of the process. More particularly, the invention relates to a process for preparing detergent compositions which are useful in automatic dishwashing machines.
Detergent compositions comprising in combination an alkali metal polyphosphate such as sodium tripolyphosphate, alkaline salts such as sodium silicate a surfactant and optionally a chlorine containing compound that provides hypochlorite ion in solution have particular utility for machine dishwashing. The production of such compositions made of agglomerates of the ingredients has been generally accomplished by the addition of an aqueous sodium silicate solution to a mixture of dry ingredients. However, compositions prepared in such manner are characterized by a tendency to cake in their cartons during storage and can also have a tendency to cake in the dispenser cups of automatic dishwashing machines. A number of process modifications have been suggested to reduce the caking tendency of detergent compositions prepared using silicate solutions as agglomerating agents. U.S. Pat. No. 2,895,916 discloses an order of addition in which a chlorine containing compound, chlorinated trisodium phosphate, is added to the composition only after the aqueous silicate has been added to an anhydrous polyphosphate. The benefit is said to result from a more rapid hydration of the sodium tripolyphosphate in the absence of chlorinated trisodium phosphate. Copending commonly assigned U.S. Ser. No. 932,107 of J. E. Davis et al discloses that a reduction in the carton caking tendency of agglomerated detergent compositions containing alkali metal polyphosphates and alkali metal silicates can be achieved if from about 2% to about 20% of a hydratable salt other than the alkali metal silicate is incorporated in the aqueous silicate solution used to agglomerate the alkali metal polyphosphate.
It has now been found that a substantial reduction in the carton caking tendency of agglomerated detergent compositions containing sodium tripolyphosphate and an alkali metal silicate can be achieved if from about 5% to about 50% of the total sodium tripolyphosphate in the composition is withheld from the agglomeration process until at least about 30% of the alkali metal silicate solution has been added.
It is an object of this invention to produce agglomerated granular detergent compositions containing sodium tripolyphosphate and alkali metal silicate which are resistant to caking.
It is another object of this invention to utilize powdered sodium tripolyphosphate with a particle size such that about 90% passes through a 100 mesh Tyler Standard screen as a substitute for a portion of granular sodium tripolyphosphate with a particle size such that less than about 10% passes through a 100 mesh Tyler Standard screen in an agglomeration process utilizing sodium tripolyphosphate and alkali metal silicate solutions.
Other objects and advantages will be apparent from the following description and examples.